Modern integrated circuits are made of literally millions of active devices such as transistors and capacitors. These devices are initially isolated from each other, but are later interconnected together to form functional circuits. Typical interconnect structures include lateral interconnections, such as metal lines (wirings), and vertical interconnections, such as vias and contacts. Interconnections are increasingly determining the limits of performance and the density of modern integrated circuits. On top of the interconnect structures, bond pads are formed and exposed on the surface of the respective die. Electrical connections are made through bond pads to connect the die to a package substrate or another die. Bond pads can be used for wire bonding or flip-die bonding. Flip-die packaging utilizes bumps to establish electrical contact between a die's input/output (I/O) pads and the substrate or lead frame of the package. Structurally, a bump structure usually refers to a bump and an “under bump metallurgy” (UBM) located between the bump and an I/O pad. Wafer level die scale packaging (WLCSP) is currently widely used for its low cost and relatively simple processes, and ball placement or ball drop process is utilized in the WLCSP technology.
Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon. Dozens or hundreds of integrated circuits are manufactured on a single semiconductor wafer. The individual dies are typically singulated by sawing the integrated circuits along a scribe line. The individual dies are then packaged separately, in multi-die modules, or in other types of packaging, for example.
The semiconductor industry continues to improve the integration density of various electronic components (e.g., transistors, diodes, resistors, capacitors, etc.) by continual reductions in minimum feature size, which allow more components to be integrated into a given area. These smaller electronic components such as integrated circuit dies also require smaller packages that utilize less area than packages of the past, in some applications. Wafer level die scale packages (WLCSP) are one type of smaller packaging devices for semiconductor devices, in which dies are packaged while still in wafer form and then are singulated.